Laser recording of digital data can be on rotating optical memory disks or optical media that is moving linearly as with optical memory cards or optical memory tape. The commercial fields for linear optical data storage include optical memory cards, two-dimensional bar codes, and digital sound on motion picture films.
The PDF-417 (Portable Data File), two-dimensional bar code has become a widely accepted way of storing data on cards, documents, and packages. It is used to encode graphics, including fingerprints. It has begun to be used as a form of postage stamp printed by a laser printer connected to a personal computer following authorization over the Internet. The PDF-417 specification was disclosed in 1991. PDF-417 utilizes images with minimum dimensions of about 150 microns. An earlier, higher resolution form of two-dimensional bar code was disclosed in U.S. Pat. No. 4,634,850 entitled, "Quad Density Optical Data Systems," assigned to Drexler Technology Corporation, which was filed Nov. 4, 1985, and issued Jan. 6, 1987. A closely related patent is U.S. Pat. No. 4,786,792 issued Nov. 22, 1988, which is also assigned to Drexler Technology corporation. These two patents relate to reading a high-resolution form of two-dimensional bar codes with image dimensions of 3 to 35 microns compared with the 150-micron image dimension of PDF-417. Examples of patents directly related to the PDF-417 system are U.S. Pat. Nos. 5,243,655, 5,304,786, and 5,319,181 filed from 1990 to 1992 and issued 1993 and 1994, which are assigned to Symbol Technologies Inc.
Three patents have been assigned to Drexler Technology Corporation which involve the laser recording on reflective optical data storage medium using a microscopic laser beam of one to a few microns in diameter to create eye-visible images formed from pixels (picture elements), which in turn are formed from groups of 4, 9, or 16 closely-spaced laser-recorded microscopic spots. These pixels are used to create visual alpha-numeric characters or images, including portrait images of people. The three Drexler Technology patents are U.S. Pat. No. 4,680,459 entitled, "Updatable Micrographic Pocket Data Card," U.S. Pat. No. 4,814,594 entitled, "Updatable Micrographic Pocket Data Card," and U.S. Pat. No. 5,421,619 entitled, "Laser Imaged Identification Card." Methods and apparatus involving linear optical data storage of data on motion picture film are described in the following seven U.S. patents. In these cases the digital optical data represents motion picture digital sound. Two of those patents, assigned to Drexler Technology, are U.S. Pat. Nos. 4,503,135 and 4,603,099. Patents assigned to Sony Corporation in this field include U.S. Pat. Nos. 5,471,263, 5,523,996, 5,543,868, and 5,666,185. One of the relevant motion picture sound patents assigned to Dolby Laboratories is U.S. Pat. No. 5,710,752.
Another relevant patent is recently-issued U.S. Pat. No. 5,932,865 assigned to Drexler Technology Corporation, which is entitled, "Anti-Counterfeit Validation Method for Electronic Cash Cards Employing an Optical Memory Stripe." Two sentences in the abstract point out the relevant features of this patent; namely, "Such counterfeiting can be inhibited by bonding an optical memory stripe to the smart card with pre-recorded or post-recorded validation data on the card. This optical validation data would be read with a photodetector array and could be transmitted to the recipient during funds transfer and/or used locally to control dispensing of cash." This patent explains the importance of laser recording data which are readable with CCD arrays, but does not disclose the method of the present invention.
Typical optical memory cards utilize a 35 mm-wide, reflective optical memory recording stripe which stores about 4 megabytes of data when 2.5 micron spots and 12 micron track-to-track spacings are used. The reader/writer device sells for about $2,500, and read-only devices for those cards are also expensive because of the precision required to track the digital data on the optical card with a low power laser diode. Customers have requested an inexpensive, read-only device for the optical memory cards, and it is believed some customers would probably accept a somewhat lower data-storage-capacity card if that would lead to an inexpensive read-only device.
It is the object of the present invention to devise a method and apparatus for laser recording of a two-dimensional bar code readable with CCD or other photodetector arrays and with data storage capacities ranging from about 15 to more than 500 times greater than that of PDF-417 bar codes. Another object is to utilize data-pixel-based two-dimensional bar codes on cards or labels for authentication, validation, authorization, or identification of Internet and Intranet transactions, documents, communications, and manufactured products. Another object of the invention is to devise a method and apparatus to make CCD-read data-pixel-based two-dimensional bar codes updatable. Another object is for an optical memory card to be utilized in reading and writing microscopic data spots during some time periods and writing and reading large data pixels with the same card during other time periods.